1. Field of Invention
The present invention relates to an etching device. More particularly, the present invention relates to an etching device capable of forming an uniform etchant film.
2. Description of Related Art
Typically, the laminate substrate used to manufacture a printed circuit board is formed by pressing together several doable-sided boards. The double-sided board comprises alternating layers of an insulating layer and two circuit layers. The method of respectively forming the circuit layers on each side of the insulating layer comprises the steps of forming a copper layer on each side of the insulating layer, and then patterning the copper layers by a photolithography process and an etching process to form a circuit layer on each side of the insulating layer, respectively.
FIG. 1A is a schematic, top view of a double-sided board when copper layers on both sides of the insulating layer are converted into circuit layers by using a conventional etching device. FIG. 1B is a cross-sectional view along a line I--I in FIG. 1A.
As shown in FIG. 1A together with FIG. 1B, a double-sided board 104 constituting alternating layers of an insulating layer 100 and copper layers 102a and 102b is provided. After performing a photolithography process, a wet etching process is performed to pattern the copper layers 102a and 102b. In the wet etching process, the double-sided board 104 is supported by several hollow sheet-type rollers 106b and contacts the hollow sheet-type rollers 106b through the copper layer 102b (as shown in FIG. 1A). While the wet etching process is performed, the hollow sheet-type rollers 106b are driven to roll by axles 106a and the double-sided board 104 levelly moves in a direction indicated by an arrow 110. Additionally, nozzles 114 spray etchant 108a onto the copper layers 102a and 102b. The etchant 108a is conically sprayed from the nozzles 114 in a swing fashion at a fixed point or in a to-and-fro horizontally fashion onto the copper layers 102a and 102b. Aternatively, the etchant 108a is sprayed from angled nozzles (not shown) in a swing fashion at a fixed point or in a to-and-fro horizontally fashion onto the copper layers 102a and 102b. Therefore, a lot of liquid 108b corresponding to the nozzles 114 is formed on the copper layer 102a to perform the wet etching process.
However, the etchant easily agglomerates to form a nonuniform etchant film 112 on the copper layer 102a, such that the thickness of the nonuniform etchant film 112 on the margin of the double-sided board 104 is larger than that in the center of the double-sided board 104. The appearance is called a fountain effect. Since thickness of the etchant film is nonuniform, the etching rate in the margin region of the double-sided board 104 is different from that of the central region of the double-sided board 104.
FIG. 2 is a contour diagram of the copper layer 102a after the etching process is performed. Obviously, the etchant film 112 in the central region of the double-sided board 104 is relatively thick, so that the etchant used in the central region of the double-sided board is not easily refreshed. Therefore, the etching result in the central region of the double-sided board 104 is relatively poor. Nevertheless, the etchant film 112 in the margin region of the double-sided board 104 is relatively thin, so that the etchant in the margin region of the double-sided board is often fresh. Hence, the etching result in the margin region of the double-sided board 104 is relatively good. Altogether, the thickness of the copper layer 102a in the central region of the double-sided board 104 is larger than that in the margin region of the double-sided board 104.
Conventionally, in order to move the double-sided board 104 along the direction indicated by arrow 110 more easily, several hollow sheet-type rollers 120 (as shown in FIG. 3) are disposed on the copper layer 102a. But the relative motion between the hollow sheet-type rollers 120 and the double-sided board 104 disrupts the flux of the etchant. Therefore, the etchant film is still nonuniform and the etching result of the copper layer 102a is still poor.
Additionally, in order to overcome the problem due to the fountain effect, another conventional etching device is provided, where the etchant is sectorially sprayed with a particular angle onto the double-sided board. Therefore, the etchant on the copper layer agglomerates to form an etchant flax. Moreover, several hollow sheet-type rollers are disposed on the double-sided board to assist the motion of the double-sided board (the cross-section of the device described above is similar to FIG. 3). However, the relative motion between the hollow sheet-type rollers and the double-sided board disrupts the flux of the etchant. Hence, the thickness of the etchant film is still nonuniform.